US20140192932A1

US20140192932A1 - Method and System for Implementing a Single Weight Spatial Multiplexing (SM) MIMO System

Info

Publication number: US20140192932A1
Application number: US14/096,667
Authority: US
Inventors: Mark Kent; Vinko Erceg; Uri M. Landau; Peter van Rooyen; Peter ROUX
Original assignee: Broadcom Corp
Current assignee: Avago Technologies International Sales Pte Ltd
Priority date: 2004-10-06
Filing date: 2013-12-04
Publication date: 2014-07-10
Also published as: US20120281794A1; US8605661B2; US20060072499A1; US8254306B2

Abstract

Certain aspects of the method may comprise generating at least one control signal that may be utilized to control at least a first of a plurality of received spatially multiplexed communication signals. An amplitude and/or phase of the first received spatially multiplexed communication signal may be adjusted via the generated control signal so that the amplitude and/or phase of the first received spatially multiplexed communication signal may be equivalent to an amplitude and/or phase of a second received spatially multiplexed communication signal. The amplitude of the first received spatially multiplexed communication signal is adjusted within the processing path used to process the first received spatially multiplexed communication signal.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS/INCORPORATION BY REFERENCE

This patent application makes reference to, claims priority to, claims benefit from, and incorporates by reference herein in its entirety U.S. patent application Ser. No. 13/554,652, filed on Jul. 20, 2012, which is a continuation of U.S. patent application Ser. No. 11/173,726 filed on Jun. 30, 2005, which claims priority to U.S. Provisional Patent Application Ser. No. 60/616,734 filed on Oct. 6, 2004.
This application makes reference to:
U.S. patent application Ser. No. 11/173,870 filed Jun. 30, 2005;
U.S. patent application Ser. No. 11/174,303 filed Jun. 30, 2005;
U.S. patent application Ser. No. 11/173,502 filed Jun. 30, 2005;
U.S. patent application Ser. No. 11/173,871 filed Jun. 30, 2005;
U.S. patent application Ser. No. 11/173,964 filed Jun. 30, 2005;
U.S. patent application Ser. No. 11/173,252 filed Jun. 30, 2005;
U.S. patent application Ser. No. 11/174,252 filed Jun. 30, 2005;
U.S. patent application Ser. No. 11/172,756 filed Jun. 30, 2005;
U.S. patent application Ser. No. 11/173,305 filed Jun. 30, 2005;
U.S. patent application Ser. No. 11/172,759 filed Jun. 30, 2005;
U.S. patent application Ser. No. 11/173,689 filed Jun. 30, 2005;
U.S. patent application Ser. No. 11/173,304 filed Jun. 30, 2005;
U.S. patent application Ser. No. 11/173,219 filed Jun. 30, 2005;
U.S. patent application Ser. No. 11/172,779 filed Jun. 30, 2005;
U.S. patent application Ser. No. 11/172,702 filed Jun. 30, 2005;
U.S. patent application Ser. No. 11/173,727 filed Jun. 30, 2005;
U.S. patent application Ser. No. 11/172,781 filed Jun. 30, 2005;
U.S. patent application Ser. No. 11/174,067 filed Jun. 30, 2005;
U.S. patent application Ser. No. 11/173,854 filed Jun. 30, 2005;
U.S. patent application Ser. No. 11/173,911 filed Jun. 30, 2005; and
U.S. patent application Ser. No. 11/174,403 filed Jun. 30, 2005.
The above referenced applications are hereby incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention
Certain embodiments of the invention relate to spatial multiplexing in a MIMO system. More specifically, certain embodiments of the invention relate to a method and system for implementing a single weight spatial multiplexing multi-input multi-output (MIMO) system.
2. Background Art
In most current wireless communication systems, nodes in a network may be configured to operate based on a single transmit and a single receive antenna. However, for many of current wireless systems, the use of multiple transmit and/or receive antennas may result in an improved overall system performance. These multi-antenna configurations, also known as smart antenna techniques, may be utilized to reduce the negative effects of multipath and/or signal interference may have on signal reception. Existing systems and/or systems which are being currently deployed, for example, CDMA-based systems, TDMA-based systems, WLAN systems, and OFDM-based systems such as IEEE 802.11a/g/n, may benefit from configurations based on multiple transmit and/or receive antennas. It is anticipated that smart antenna techniques may be increasingly utilized both in connection with the deployment of base station infrastructure and mobile subscriber units in cellular systems to address the increasing capacity demands being placed on those systems. These demands arise, in part, from a shift underway from current voice-based services to next-generation wireless multimedia services that provide voice, video, and data communication.
The utilization of multiple transmit and/or receive antennas is designed to introduce a diversity gain and array gain and to suppress interference generated within the signal reception process. Such diversity gains improve system performance by increasing received signal-to-noise ratio, by providing more robustness against signal interference, and/or by permitting greater frequency reuse for higher capacity. In communication systems that incorporate multi-antenna receivers, a set of M receive antennas may be utilized to null the effect of (M−1) interferers. Accordingly, N signals may be simultaneously transmitted in the same bandwidth using N transmit antennas, with the transmitted signal then being separated into N respective signals by way of a set of N antennas deployed at the receiver. Systems that utilize multiple transmit and multiple receive antenna may be referred to as multiple-input multiple-output (MIMO) systems. One attractive aspect of multi-antenna systems, in particular MIMO systems, is the significant increase in system capacity that may be achieved by utilizing these transmission configurations. For a fixed overall transmitted power, the capacity offered by a MIMO configuration may scale with the increased signal-to-noise ratio (SNR).
However, the widespread deployment of multi-antenna systems in wireless communications, particularly in wireless handset devices, has been limited by the increased cost that results from increased size, complexity, and power consumption. The necessity of providing a separate RF chain for each transmit and receive antenna is a direct factor in the increased the cost of multi-antenna systems. Each RF chain generally comprises a low noise amplifier (LNA), a filter, a downconverter, and an analog-to-digital converter (A/D). In certain existing single-antenna wireless receivers, the single required RF chain may account for over 30% of the receiver's total cost. It is therefore apparent that as the number of transmit and receive antennas increases, the system complexity, power consumption, and overall cost may increase.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present invention as set forth in the remainder of the present application with reference to the drawings.

BRIEF SUMMARY OF THE INVENTION

A method and/or system for implementing a single weight spatial multiplexing multi-input multi-output (MIMO) system, substantially as shown in and/or described in connection with at least one of the figures, as set forth more completely in the claims.
These and other advantages, aspects and novel features of the present invention, as well as details of an illustrated embodiment thereof, will be more fully understood from the following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

FIG. 1 is a block diagram of a configuration of an exemplary single weight spatially multiplexed MIMO system, in accordance with an embodiment of the invention.

FIG. 2 is a block diagram of an exemplary single weight single channel system for WCDMA, in accordance with an embodiment of the invention.

FIG. 3 is a block diagram of a direct conversion radio block that may be utilized in accordance with an aspect of the invention.

FIG. 4A is a block diagram of an exemplary baseband processor that may be utilized within a MIMO system, in accordance with an aspect of the invention.

FIG. 4B illustrates an exemplary maximum-ratio combining (MRC) block, in accordance with an embodiment of the invention.

FIG. 5 is a block diagram of an exemplary receiver illustrating spatial multiplexing in a MIMO communication system that may be utilized in connection with an embodiment of the invention.

FIG. 6 is a flow diagram illustrating exemplary steps for processing signals in a receiver, in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Certain aspects of the method may comprise generating at least one control signal that may be utilized to control at least a first of a plurality of received spatially multiplexed communication signals. An amplitude of the first received spatially multiplexed communication signal may be adjusted via the generated control signal so that the amplitude of the first received spatially multiplexed communication signal may be equivalent to an amplitude of a second received spatially multiplexed communication signal. The amplitude of the first received spatially multiplexed communication signal is adjusted within the processing path used to process the first received spatially multiplexed communication signal. A phase of the first received spatially multiplexed communication signal may be adjusted via the generated control signal so that the phase of the first received spatially multiplexed communication signal may be equivalent to a phase of a second received spatially multiplexed communication signal. The phase of the first received spatially multiplexed communication signal may be adjusted within a processing path used to process the first received spatially multiplexed communication signal.
The generated control signal may comprise a single weight signal. The amplitude of the first received spatially multiplexed communication signal may be adjusted continuously and/or at discrete intervals. The first received spatially multiplexed communication signal may be amplified so that a gain of the first received spatially multiplexed communication signal may be equivalent to a gain of the second received spatially multiplexed communication signal. The amplitude-adjusted first received spatially multiplexed communication signal may be combined with the second received spatially multiplexed communication signals to generate a combined received spatially multiplexed communication signal. A plurality of baseband combined channel estimates of a time varying impulse response for the plurality of received spatially multiplexed communication signals may be generated and the baseband combined channel estimates of the time varying impulse response may be utilized to generate a plurality of control signals. The control signals may be generated utilizing one or more optimization algorithms, such as a maximum signal-to-noise ratio (SNR) algorithm, a maximum signal-to-interference-and-noise ratio (SINR) algorithm, and/or a minimum bit error rate (BER) algorithm.
Spatial multiplexing (SM) may provide a mode of signal transmission predicated upon the use of multiple antennas at both a transmitter and a receiver, for example, in such a way that the capacity of a wireless radio link may be increased without correspondingly increasing power or bandwidth consumption. In a case in which N antennas are used at both a transmitter and a receiver, an input stream of information symbols provided to the transmitter is divided into N independent substreams. Spatial multiplexing contemplates that each of these N independent substreams may occupy the same “space-time channel”, for example, time slot, frequency, or code/key sequence, of the applicable multiple-access protocol. Within the transmitter, each substream may be separately applied to the N transmit antennas and propagated over an intervening multipath communication channel to a receiver. Error correction coding may be applied to each of the N streams separately or in a combined space-time methodology.
The composite multipath signals may then be received by an array of N or more receive antennas deployed at the receiver. At the receiver, a “spatial signature” defined by the N phases and N amplitudes arising at the receive antenna array for a given substream may be then estimated. Signal processing techniques may be then applied in order to spatially separate the received signals, which may allow the original substreams to be recovered and synthesized into the original input symbol stream. An overall system capacity of the order of the minimum of M and N, min(M,N), for example, may be achieved, where M may be the number of receive antennas and N may be the number of transmit antennas for flat fading channel conditions. The principles of spatially multiplexed communication and exemplary system implementations are further described in, for example, “Optimum combining for indoor radio systems with multiple users”, by J. H. Winters, IEEE Transactions on Communications, Vol. COM-35, No. 11, November 1987, which is hereby incorporated by reference in its entirety.
FIG. 1 is a block diagram of an exemplary single weight spatially multiplexed MIMO system, in accordance with an embodiment of the invention. Referring to FIG. 1, there is shown a transceiver 100. The transceiver 100 may comprise a plurality of transmit antennas 122 _{1 . . . N}, a plurality of receive antennas 124 _{1 . . . M}, a plurality of band pass filters (BPFs) 126 _{1 . . . M}, a low noise amplifier 128, a plurality of phase shifter/LNA (PSLNA) blocks 130 _{1 . . . M-1}, a plurality of direct conversion radio (DCR) blocks 132 _{1 . . . P}, a plurality of analog-to-digital (A/D) converters 134 _{1 . . . P}, a plurality of summers 136 _{1 . . . P}, a spatially multiplexed baseband processor (SMBB) 138 and a single weight generator (SWG) 140.
The plurality of transmit antennas 122 _{1 . . . N}may transmit processed spatially multiplexed RF signals to a plurality of receive antennas 124 _{1 . . . M}. On the receive side, the plurality of BPFs 126 _{1 . . . M}may comprise suitable logic, circuitry, and/or code and may be adapted to receive a plurality of spatially multiplexed RF signals from the plurality of receive antennas 124 _{1 . . . M}. The plurality of BPFs 126 _{1 . . . M}may then limit frequencies of the received spatially multiplexed signals to a pre-determined band of frequencies, and output that band of frequencies to the LNA 128 and the plurality of PSLNA blocks 130 _{1 . . . M-1}. The advantage of spatially multiplexing techniques lies in the fact that the same bandwidth may be used for all the transmit data streams. The LNA 128 and the plurality of PSLNA blocks 130 _{1 . . . M-1}may comprise suitable logic, circuitry, and/or code and may be adapted to receive a plurality of input signals, amplify the signals and adding phase shifts while introducing very little additional noise or distortion. In addition, the LNA within the PSLNA blocks 130 _{1 . . . M-1}may be adapted to receive as an input an amplified signal, shift the phase of the signal, and generate a resulting output phase-shifted signal. The plurality of PSLNA blocks 130 _{1 . . . M-1}may be adapted to receive a plurality of SW control signals 142 ₁₁to 142 _PM-1from SWG 140 to modify the phase and/or amplitude of the plurality of received spatially multiplexed communication signals.
The plurality of DCR blocks 132 _{1 . . . P}may comprise suitable logic, circuitry and/or code and may be adapted to amplify and convert the received analog RF signal down to baseband. For example, the DCR block 132 ₁may utilize a number of amplifier stages implemented with for example, LNAs, a complex in-phase and quadrature signal component mixer, and/or a low pass channel filter. The plurality of A/D converters 134 _{1 . . . P}may comprise suitable logic, circuitry, and/or code that may be adapted to receive an analog signal from the plurality of DCR blocks 132 _{1 . . . P}and generate a corresponding output digital signal, which may be communicated to the SMBB 138. The digital signal may sample the analog signal at a pre-defined rate.
The SMBB 138 may comprise, for example, suitable logic, circuitry and/or code that may be adapted to perform baseband processing. The SMBB 138 may perform, for example, demodulation, decoding and spatial demultiplexing on the received baseband signals. The SMBB 138 may be adapted to receive a plurality of digital RF signals from the plurality A/D converters 134 _{1 . . . P}and generate a plurality of baseband combined channel estimates ĥ ₁to ĥ _Pand a plurality of channel estimates {circumflex over (X)}₁to {circumflex over (X)}_Pof the original channel over which the input signals X₁to X_P, propagate. The spatial multiplexing processor 138 may be adapted to separate the different space-time channels utilizing a Bell Labs Layered Space-Time (BLAST) algorithm, for example, by performing sub-stream detection and sub-stream cancellation. The transmission capacity may be increased almost linearly by utilizing the BLAST algorithm and assuming good channel estimation and cancellation.
The SWG 140 may include, for example, suitable logic, circuitry and/or code that may be adapted to determine the phase and/or the amplitude utilized in combining the received spatially multiplexed communication signals from the plurality of receive antennas 124 _{1 . . . M}. The SWG 140 may generate SW control signals that may be utilized to tune the amplitude and phase shifters of the PSLNA blocks 130 _{1 . . . M-1}. The SWG 140 may generate the signal based on, for example, one or more of the following optimization algorithms: maximum signal-to-noise ratio (SNR), maximum signal-to-interference-and-noise ratio (SINR), minimum bit error rate (BER) and/or other optimization algorithms. The SWG block 140 may be adapted to receive a plurality of baseband combined channel estimates ĥ ₁to ĥ _Pfrom the SMBB 138. The SWG block 140 may be adapted to generate a plurality of single weight control signals 142 ₁₁to 142 _PM-1to modify the phase and/or amplitude of the plurality of received spatially multiplexed communication signals.
In one aspect of the invention, the plurality of PSLNA blocks 130 _{1 . . . M-1}may be utilized to shift the phase of the spatially multiplexed signals received at antennas 124 _{2 . . . M}so that it is in-phase with the signal received at antenna 124 ₁. For example, the PSLNA block 130 ₁may receive a single weight (SW) control signal A₁₁, φ₁₁ 142 ₁₁, which may be generated by the single weight generator (SWG) 140. The PSLNA block 130 ₁may then shift the phase of the signal received at antenna 124 ₂based on the received SW control signal 142 ₁₁. In this regard, the signals received at antennas 124 ₁to 124 _Mfor the first substream may be in phase at summer 136 ₁. The following sub streams (2 to P) may also be in phase at each of the corresponding summer blocks (2 to P). In addition, the LNA within the PSLNA block 130 ₁and the LNA 128 may amplify the respective signals received from antennas 124 ₁and 124 _Mso that balanced gain is achieved for both signals at summer 136 ₁.
The plurality of PSLNA blocks 130 _{2 . . . M-1}may each receive a single weight (SW) control signal A₁₂, φ₁₂ 142 ₁₂to A_1M-1, φ_1M-1 142 _M-1, which may be generated by the single weight generator (SWG) 140. The outputs generated by the plurality of PSLNA blocks 130 _{2 . . . M-1}may be summed by the summer 136 ₁, which generates a RF signal to the DCR block 132 ₁. The DCR block 132 ₁may comprise suitable logic, circuitry and/or code and may be adapted to amplify and convert the received analog RF signal down to baseband. The A/D converter 134 ₁may comprise suitable logic, circuitry, and/or code that may be adapted to receive an analog signal from the DCR block 132 ₁and generate a corresponding output digital signal, which may be communicated to the spatially multiplexed baseband processor (SMBB) 138. The SMBB 138 may be adapted to generate an estimate {circumflex over (X)}₁of the original input signal X₁. Similarly, the SMBB 138 may be adapted to generate a plurality of estimates {circumflex over (X)}₂to {circumflex over (X)}_Pof the original input signals X₂to X_P.
The SMBB 138 may be adapted to generate a plurality of baseband combined channel estimates ĥ ₁to ĥ _Pto the SWG block 140. The SWG block 140 may be adapted to generate a plurality of SW control signals 142 ₁₁to 142 _1M-1to the plurality of PSLNA blocks 130 _{1 . . . M-1}for the first RF path to generate the estimate {circumflex over (X)}₁of the original input signal X₁. Similarly, the SWG block 140 may be adapted to generate a plurality of SW control signals 142 ₂₁to 142 _PM-1to the plurality of PSLNA blocks 130 _{1 . . . M-1}for the successive RF paths to generate the plurality of estimates {circumflex over (X)}₂to {circumflex over (X)}_Pof the original input signals X₂to X_P. The plurality of SW control signals may be generated utilizing one or more optimization algorithms, such as a maximum signal-to-noise ratio (SNR) algorithm, a maximum signal-to-interference-and-noise ratio (SINR) algorithm, and/or a minimum bit error rate (BER) algorithm.
FIG. 2 is a block diagram of an exemplary single weight single channel system for WCDMA, in accordance with an embodiment of the invention. Referring to FIG. 2, the single weight single channel system 200 for WCDMA may comprise a transmitter section 200 a and a receiver section 200 b. The transmitter section 200 a may comprise a mixer 201 and antenna 203. Data input x₁and code c₁are inputs to the mixer 201. The receiver section 200 b may comprise antennas 205 and 207, bandpass filters (BPF) 202 and 206, low noise amplifier (LNA) 204, phase shifter/LNA (PSLNA) block 208, a direct conversion radio (DCR) block 212, an analog-to-digital (A/D) converter 214, a baseband processor 216, and a single weight generator (SWG) 218.
On the transmit side, the mixer 201 may be adapted to mix the data input x₁with code c₁. The actual time varying impulse response of the channel is represented by h₁and h₂per base station. The estimates of the actual time varying impulse response of the channel are represented by ĥ₁and ĥ₂per base station.
On the receive side, the BPFs 202 and 206 may comprise suitable logic, circuitry, and/or code and may be adapted to receive as an input an RF signal from the antennas 205 and 207, respectively. The BPFs 202 and 206 may then limit the frequencies of the signal to a pre-determined band of frequencies, and output that band of frequencies to the LNA 204 and the PSLNA block 208. The LNA 204 and the PSLNA block 208 may comprise suitable logic, circuitry, and/or code and may be adapted to receive as an input a signal, and amplify the signal while introducing very little additional noise. In addition, the LNA within the PSLNA block 208 may be adapted to receive as an input an amplified signal, shift the phase of the signal, and output a resulting phase-shifted signal.
In one aspect of the invention, the PSLNA block 208 may be utilized to shift the phase of the signal received at antenna 207 so that it is in-phase with the signal received at antenna 205. For example, the PSLNA block 208 may receive a single weight (SW) control signal 220, which may be generated by the single weight generator (SWG) 218. The PSLNA block 208 may then shift the phase of the signal received at antenna 207 based on the received SW control signal 220. In this regard, the two signals received at antennas 205 and 207 may be in phase at point 210. In addition, the LNA within the PSLNA block 208 and the LNA 204 may amplify the respective signals received from antennas 207 and 205 so that balanced gain is achieved for both signals at point 210.
The DCR block 212 may comprise suitable logic, circuitry and/or code and may be adapted to amplify and convert the received analog RF signal down to baseband. For example, the DCR block 212 may utilize a number of amplifier stages implemented with LNAs, a complex in-phase and quadrature signal component mixer, and a low pass channel filter. The A/D converter 214 may comprise suitable logic, circuitry, and/or code that may be adapted to receive an analog signal from the DCR block 212 and generate a corresponding output digital signal, which may be communicated to the baseband processor 216. The digital signal may sample the analog signal at a pre-defined rate.
The baseband processor 216 may comprise suitable logic, circuitry and/or code that may be adapted to process a digital signal and generate a voice output signal 222 and a data output signal 224. In addition, the baseband processor 216 may be adapted to generate output signals that may be utilized by the SWG block 218 for generating the SW 220 for control of the phase shifting in the PSLNA block 208. The voice output signal 222 may be further processed by a voice processing unit and/or a digital display processor, respectively, for example.
The SWG block 218 may comprise suitable circuitry, logic, and/or code and may be adapted to process channel function estimates and RF signal timing information received from the baseband processor 216, for example, and generate a single weight (SW) 220. The SW 220 may be utilized by the PSLNA block 208 to phase-shift an RF signal received at antenna 207 and generate an RF signal that is in-phase with a signal received at antenna 205.
In operation, the transmitter side 200 a may be adapted to mix the input data signal x₁with the code signal c₁and then transmitted the signal via antenna 203 over the air. As the signal is transmitted over the air, it may traverse a plurality of different paths or multipaths due to reflections. The actual time varying impulse response of the channel over which the signals traverse is represented by h₁and h₂per base station. The estimates of the actual time varying impulse response of the channel are represented by ĥ₁and ĥ₂per base station. The transmitted signal may then be received via various paths where actual time varying impulse response of the channel is represented by h₁and h₂per base station. The signal received by the antennas 205 and 207 may be bandpass filtered by BPFs 202 and 206, respectively, and amplified by the LNA 204 and the PSLNA block 208, respectively. In addition, the PSLNA block 208 may receive SW control signal 220 from the SWG block 218 and may adjust the phase of the signal received at antenna 207 based on the SW 220. In this regard, the signal received at antenna 207 may be in-phase with the signal received at antenna 205. In addition, the gains of the two signals received at antennas 205 and 207 may be adjusted so that there may be a gain balance at point 210 in the receiver side 200 b.
The RF signal may then be processed by the DCR block 212 and may be further amplified, mixed with a VCO signal, and/or low pass filtered. The RF analog signal processed by the DCR block may be converted to a digital signal by the A/D 214. The digital output of the A/D 214 may be communicated as an input to the baseband processor 216. The baseband processor 216 may further process the input to generate a voice signal 222 and a data signal 224. The voice signal 222 may be further processed, for example, by a voice processing system, and the data signal 224 may be further processed by a display processor, for example. In addition, the baseband processor 216 may be adapted to generate signals that may be utilized by the SWG 218 for generating the signal SW 220.
Even though the transmit side 200 a utilizes one antenna 203, the present invention may not be limited in this regard and multiple transmit antennas may be utilized in accordance with various aspects of the invention. Similarly, in accordance with a different aspect of the invention, multiple receive antennas may be utilized on the receive side 200 b. In addition, even though phase adjustment techniques utilizing a single weight value on one or more signals is implemented on the receive side 200 b, the invention is not so limited. Phase adjustment techniques in accordance with the present invention, utilizing a single weight value on one or more signals may also be implemented on the transmit side 200 a.
FIG. 3 is a block diagram of a direct conversion radio block that may be utilized in accordance with an aspect of the invention. Referring to FIG. 3, the direct conversion radio (DCR) block 300 may comprise suitable logic, circuitry, and/or code and may be adapted to amplify and convert the received analog RF signal down to baseband. In an exemplary aspect of the invention, the DCR block 300 may comprise an LNA 304, a voltage controlled oscillator (VCO) 308, a mixer 306, and a low pass filter (LPF) 312.
The LNA 304 may receive an RF signal 302 and amplify it based on a determined gain level. The VCO 308 may comprise suitable logic, circuitry and/or code and may be adapted to output a signal of a specific frequency which may be pre-determined, or controlled by a voltage signal input to the VCO. The VCO signal may be mixed by the mixer 306 with the amplified signal received from the LNA 304. The LPF 312 may comprise suitable logic, circuitry and/or code and may be adapted to receive the mixed signal from the mixer 306, limit the frequencies of the mixed signal to a determined range of frequencies up to a certain upper limit frequency, and output that range of frequencies as a baseband signal 314.
FIG. 4A is a block diagram of an exemplary baseband processor that may be utilized within a MIMO system, in accordance with an aspect of the invention. Referring to FIG. 4A, the baseband processor 400 may comprise a cluster path processor (CPP) block 432, a maximum ratio combining (MRC) block 424, a despreader block 426, a diversity processor block 428, a macrocell combiner block 430, a bit rate processing block 431, a convolutional decoder block 438, and a turbo decoder block 440.
U.S. application Ser. No. 11/173,854 provides a detailed description of signal clusters and is hereby incorporated herein by reference in its entirety.
The CPP block 432 may comprise a plurality of cluster processors that may be adapted to receive and process an input signal 402 received from a chip matched filter (CMF), for example. In the baseband receiver processor 400, the CPPs 432 a, . . . , 432 n within the CPP block 432 may be partitioned into pairs of processors, wherein each pair of processor may be adapted to track time-wise and estimate the complex phase and amplitude of the element in the cluster. A cluster may comprise an aggregate of received multipath signals with maximum (max) time difference that may be no more than 16×1/3.84e6 seconds, for example. Under these circumstances, the need for two processors may be derived from the fact that the WCDMA standard facilitates a receiving mode in which the transmitted signal is transmitted over two antennas, which necessitates the two processors. These receiving modes comprise close loop 1 (CL1), close loop 2 (CL2), and STTD. The CPP block 432 may be adapted to determine estimates of the entire transfer function of the channel and may recover channels on a per base station basis.
The CPP block 432 may be adapted to generate channel estimates ĥ₁and ĥ₂of the actual time varying impulse response of the channel per base station. The CPP 432 may also generate timing information T on per base station basis related to signals received by antennas at the receive side, such as antennas 205 and 207 of FIG. 2, for example. Corresponding lock indicators L₁and L₂may also be generated by the cluster processors. The lock indicators may provide an indication of which components in the corresponding estimates comprise valid component values. In one embodiment of the invention, cluster path processors 432 a, . . . , 432 n may be configured to operate in pairs when a transmitted signal is transmitted by two antenna, where the two antenna may be located in the same base station, or at different base stations. The channel estimates ĥ₁and ĥ₂of the actual time varying impulse response of the channel per base station, as well as lock indicators L1 and L2, and the timing information T per base station may be communicated to a single weight generation (SWG) block, for example, as well as to the maximum-ratio combining (MRC) block 424 for further processing. The channel estimates ĥ₁and ĥ₂, the lock indicators L1 and L2, and the timing information T may be utilized by an SWG block for generating a single weight (SW) control signal for phase shifting of one or more signals received by receiver antennas.
The maximum-ratio combining block 424 may comprise suitable logic, circuitry and/or code to receive timing reference signals, T, and channel estimates and lock indicators, (ĥ1,L1) and (ĥ2,L2), from the corresponding cluster path processor block 432, which may be utilized by the maximum-ratio combining block 424 to process received signals from a chip matched filter (CMF) block, for example. The maximum ratio combining block 424 may utilize channel estimate components that are valid in accordance with the corresponding lock indicator. Channel estimate components that are not valid, in accordance with the corresponding lock indicator, may not be utilized. The maximum-ratio combining block 424 may be adapted to provide a combining scheme or mechanism for implementing a rake receiver which may be utilized with adaptive antenna arrays to combat noise, fading, and/or co-channel interference.
In accordance with an embodiment of the invention, the maximum-ratio combining block 424 may comprise suitable logic, circuitry, and/or code that may be adapted to add individual distinct path signals, received from the assigned RF channel, together in such a manner to achieve the highest attainable signal to noise ratio (SNR). The highest attainable SNR may be based upon a maximum ratio combiner. A maximum ratio combiner is a diversity combiner in which each of multipath signals from all received multipaths are added together, each with unique gain. The gain of each multipath before summing can be made proportional to received signal level for the multipath, and inversely proportional to the multipath noise level. Each of the maximum-ratio combining blocks may be also adapted to utilize other techniques for signal combining such selection combiner, switched diversity combiner, equal gain combiner, or optimal combiner.
In one embodiment of the invention, the assignment of fingers in the maximum-ratio combining block 424 may be based on channel estimates h1 and h2 from the cluster path processor block 432. The proportionality constants utilized in the maximum-ratio combining block 424 may be based on the valid channel estimates, ĥ1 and ĥ2, from the cluster path processor block 432.
The despreader (DS) block 426 may comprise a plurality of despreader blocks 426 a, . . . , 426 n. Each of the despreader blocks 426 a, . . . , 426 n may comprise suitable logic, circuitry, and/or code that may be adapted to despread received signals that may have been previously spread through the application of orthogonal spreading codes in the transmitter. Prior to transmission of an information signal, known as a “symbol”, the transmitter may have applied an orthogonal spreading code that produced a signal comprising a plurality of chips. The DS block 426 may be adapted to generate local codes, for example Gold codes or orthogonal variable spreading factor (OVSF) codes, that may be applied to received signals through a method that may comprise multiplication and accumulation operations. Processing gain may be realized after completion of integration over a pre-determined number of chips in which the symbol is modulated.
Following despreading at the receiver, the original symbol may be extracted. WCDMA may support the simultaneous transmission of a plurality of spread spectrum signals in a single RF signal by utilizing spreading codes among the spread spectrum signals which are orthogonal to reduce multiple access interference (MAI). The receiver may extract an individual symbol from the transmitted plurality of spread spectrum signals by applying a despreading code, which may be equivalent to the code that was utilized for generating the spread spectrum signal. Similarly to the CPP block 432 and the MRC block 424, the DS block 426 may be assigned on a per base station basis, with the MRC block 424 communicating with the DS block 426 that may be assigned to the same base stations.
The diversity processor 428, comprising a plurality of diversity processor blocks 428 a, . . . , 428 n, may comprise suitable logic, circuitry, and/or code that may be adapted to combine signals transmitted from multiple antennas in diversity modes. The diversity modes may comprise OL, CL1 and CL2. The diversity processor 428 may combine signals transmitted from multiple antennas that are located at the same base station. Similarly with the cluster path processors 432, the maximum-ratio combining blocks 424, and the despreader blocks 426, the diversity processors 428 may be assigned on a per base station basis, with the diversity processors 428 communicating with despreader blocks 426 that may be assigned to the same base stations.
The macrocell combiner 430 may comprise suitable logic, circuit and/or code and may be adapted to achieve macroscopic diversity. The macroscopic diversity scheme may be utilized for combining two or more long-term lognormal signals, which may be obtained via independently fading paths received from two or more different antennas at different base-station sites. The microscopic diversity schemes may be utilized for combining two or more short-term Rayleigh signals, which are obtained via independently fading paths received from two or more different antennas but only one receiving site.
The bit rate processing block 431 may comprise suitable logic, circuitry and/or code to process frames of data received from the macrocell combiner 430. The processing may further comprise depuncturing, and deinterleaving data in the received frame, and further determining a rate at which processed frames are communicated in output signals.
The convolutional decoder 438 may comprise suitable logic, circuitry and/or code that may be utilized to handle decoding of convolutional codes as indicated in the 3GPP specification. The output of the convolutional decoder 438 may be a digital signal, which comprises voice information, suitable for processing by a voice-processing unit. The turbo decoder 440 may comprise suitable logic, circuitry and/or code that may be utilized to handle decoding of turbo codes as indicated in the 3GPP specification. The output of the turbo decoder 440 may be a digital signal, which has data information, such that it may be suitable for use by a video display processor.
Referring to FIGS. 2 and 4A, in operation, the transmitter side 200 a may be adapted to mix the input data signal x₁with the code signal c₁and generate the output signal, which may be transmitted via antenna 203 over different paths over the air. Each over the air path or channel has a corresponding time varying impulse response function h₁and h₂. The channel estimates ĥ₁and ĥ₂provide estimates of the actual time varying impulse response of the channel over which the received signals are transmitted. The signal received by the antennas 205 and 207 may be bandpass filtered by BPFs 202 and 206, respectively, and amplified by the LNA 204 and the PSLNA block 208, respectively. In addition, the PSLNA block 208 may receive SW control signal 220 from the SWG block 218 and may adjust the phase of the signal received at antenna 207 based on the SW 220. In this regard, the signal received at antenna 207 may be in-phase with the signal received at antenna 205. In addition, the gains of the two signals received at antennas 205 and 207 may be adjusted so that there may be a gain balance at point 210 in the receiver side 200 b.
The RF signal may then be processed by the DCR block 212 and may be further amplified, mixed with a VCO signal, and/or low pass filtered. The RF analog signal processed by the DCR block may be converted to a digital signal by the A/D 214. The digital output of the A/D 214 may be communicated as an input to the baseband processor 216. The baseband processor 216 may further process the input to generate a voice signal 222 and a data signal 224. The voice signal 222 may be further processed, for example, by a voice processing system or device, and the data signal 224 may be further processed by a display processor, for example. In addition, the baseband processor 216 may be adapted to generate signals that may be utilized by the SWG 218 in generating the signal SW 220.
The digital signal output from the A/D block 214 may be communicated as input signal 402 to the CPP block 432. For example, processor 432 a may generate a set of channel estimates and lock indicators, (ĥ1,L1), and a timing reference signal T1. Processor 432 b may generate a set a channel estimates and lock indicators, (ĥ2,L2), and a timing reference signal T2. Processor 432 a and processor 432 b may generate channel estimates and timing reference signals based on received signals from a single base station. There may be a deterministic relationship between the timing reference signals such that given, for example, T1, it may be possible to determine T2, and/or vice versa. In such case, only one timing reference signal, T, which may be based on at least one of T1 or T2, may be communicated to the maximum-ratio combining block 424.
The maximum-ratio combining block 424 may be adapted to utilize the channel estimates and lock indicators (ĥ1,L1), (ĥ2,L2) and timing information T per base station to assign rake fingers to received individual distinct path signals and to assign proportionality constants to each finger. Received individual distinct path signals may be processed in the maximum-ratio combining block 424 as signal clusters comprising a plurality of received individual distinct path signals. In an embodiment of the invention, the maximum-ratio combining block 424 may assign a time, T(n), to the nth grid element of the CPP 432, where the plurality of times T(n) may be based on the timing reference T. Given a time assignment, and a time offset, toff, a given CPP 432, n, may detect an individual distinct path signal that is received during a time interval starting at [T(n)−toff/2], and ending at [T(n)+toff/2].
The individual distinct path signals received collectively for each CPP 432 may constitute a signal cluster. The relationship of the values T(n) among the processing elements of the CPP 432 in the receiver may be such that T(n+1)−T(n) is equal to a constant value for values of n among the set of fingers. Thus, once T is determined, the timing relationships for the receipt of the plurality of individual distinct path signals constituent in the signal cluster may be determined. The time offset value, toff, may represent a time duration, which is at least as long as the period of time required for transmitting the plurality of chips contained in a symbol. For example, if the symbol comprises 16 chips, and the W-CDMA chip rate is 3.84×106 chips/second, then the time offset toff may be (16/3.84×106) seconds or approximately 4 microseconds.
Embodiments of the invention may not be limited to values of the difference T(n+1)−T(n) being constant among all n fingers in a rake receiver. However, each value, T(n), may be based on the timing reference signal, T.
The maximum-ratio combining block 424 may proportionately scale and add the received individual distinct path signals to produce a chip level output, which may be communicated to the despreader block 426. The despreader block 426 may be adapted to despread the chip level signal received from the maximum-ratio combining block 424 to generate estimates of the original transmitted signals. The diversity processor block 428 may be adapted to provide diversity processing and to generate output data estimates on a per base station basis. The macrocell combiner block 430 may achieve macroscopic diversity when a received signal has been transmitted by a plurality of base stations. The bit rate processing block 431 may perform processing tasks comprising depuncture and deinterleave on received frames of data that are communicated in received individual distinct path signals. The bit rate processing block 431 may determine a rate at which to communicate processed frames of data to the convolutional decoder block 438, and/or the turbo decoder block 440. The convolution decoder block 438 may be adapted to perform convolutional decoding on the voice portion of the signal generated from an output of the bit rate processing block 431. The turbo decoder block 440 may be adapted to perform turbo decoding on the data portion of the signal generated from an output of the bit rate processing block 431.
FIG. 4B illustrates an exemplary maximum-ratio combining (MRC) block, in accordance with an embodiment of the invention. Referring to FIG. 4B, the maximum-ratio combining (MRC) block 400 b may comprise a plurality of adders 402 b, . . . , 406 b, a plurality of multipliers 408 b, . . . , 414 b, and a plurality of delay blocks 416 b, . . . , 420 b. In one embodiment of the invention, the MRC block 400 b may receive a plurality of channel estimates h_ik(i=0, 1, . . . , L−1) from a corresponding cluster path processor block. For example, the MRC block 400 b may receive estimate vectors ĥ1 and ĥ2 of the actual time varying impulse response of a channel, from a cluster path processor. Each of the estimate vectors ĥ1 and ĥ2 may comprise a cluster grid of channel estimates h_ik(i=0, 1, . . . , L−1), where L may indicate the width of the cluster grid of estimates and may be related to the delay spread of the channel.
In operation, the MRC block 400 b may be adapted to implement the following equation:
${mrc}_{k} = \sum_{i = 0}^{L - 1} h_{L - 1 - i} \cdot {rx}_{k - i},$
where mrc_kis the output of the MRC block 400 b, hL−1−I is the plurality of channel estimates corresponding to a channel estimate vector, such as ĥ1 and ĥ2, and rx_kis a filtered complex input signal. The MRC block 400 b may be adapted to add individual distinct path signals together in such a manner to achieve a high signal to noise ratio (SNR) in an output signal mrc_k.
The MRC block 400 b may receive a filtered complex signal rx_kfrom a chip matched filter (CMF), for example. The filtered complex signal rx_kmay comprise in-phase (I) and quadrature (Q) components of a received signal. Furthermore, the filtered complex signal rx_kmay be gated by cluster path processor (CPP) output strobes derived from a CPP timing reference, for example. Channel estimates h_k(i=0, 1, . . . , L−1) may be applied to the CMF output rx_kbeginning with the last in time, hL−1, and proceeding with channel estimates hL−2, . . . , h0, utilizing multiplier blocks 408 b, . . . , 414 b, respectively. The filtered complex input signal rx_kmay be continuously delayed by delay blocks 416 b, . . . , 420 b. Each delayed output of the delay blocks 416 b, . . . , 420 b may be multiplied by the multiplier blocks 410 b, . . . , 414 b, respectively, utilizing corresponding channel estimates h_ik. The outputs of the multipliers 402 b, . . . , 406 b may be added to generate the output signal mrc_k, thereby implementing the above-referenced MRC equation.
FIG. 5 is a block diagram of an exemplary receiver illustrating spatial multiplexing in a MIMO communication system that may be utilized in connection with an embodiment of the invention. Referring to FIG. 5, there is shown a receiver 500 that comprises a plurality of receive antennas 510 _{1, 2, . . . , M}, a plurality of amplifiers 512 _{1, 2, . . . , M}, a SWG block 514, a plurality of filters 520 _{1, 2, . . . , N}, a local oscillator 522, a plurality of mixers 524 _{1, 2, . . . , N}, a plurality of analog to digital (A/D) converters 526 _{1, 2, . . . , N}and a spatial multiplexing baseband processor SMBB 530.
The antennas 510 _{1, 2, . . . , M}may be adapted to receive the transmitted signals. The amplifiers 512 _{1, 2, . . . , M}may be adapted to amplify the M received input signals. The SWG block 514 may comprise a plurality of amplitude and phase shifters to compensate for the phase difference between various received input signals. Weights may be applied to each of the input signals A_{1 . . . M}to modify the phase and amplitude of a portion of the transmitted signals received by the plurality of receive antennas 512 _{1 . . . M}and generate a plurality of output signals RF_{1 . . . N}. The plurality of filters 520 _{1, 2, . . . , N}may be adapted to filter frequency components of the RF substreams. The mixers 524 _{1, 2, . . . , N}may be adapted to downconvert the analog RF substreams to baseband. The local oscillator 522 may be adapted to provide a signal to the mixers 524 _{1, 2, . . . , N}, which is utilized to downconvert the analog RF substreams to baseband. The analog to digital (A/D) converters 526 _{1, 2, . . . , N}may be adapted to convert the analog baseband substreams into their corresponding digital substreams. The spatial multiplexing baseband processor SMBB 530 may be adapted to process the digital baseband substreams and multiplex the plurality of digital signals to generate output signals or symbols {circumflex over (X)}₁. . . {circumflex over (X)}_Nwhich may be estimates of the original spatial multiplexing sub-stream signals or symbols X₁. . . X_N.
In operation, the MT RF signals transmitted by a plurality of transmitters may be received by a plurality of M receive antennas 510 _{1, 2, . . . , M}deployed at the receiver 500. Each of the M received signals may be amplified by a respective low noise amplifier 512 _{1, 2, . . . , M}. A plurality of weights may be applied to each of the input signals A_{1 . . . M}to modify the phase and amplitude of a portion of the transmitted signals received by the plurality of receive antennas 512 _{1 . . . M}. A plurality of output signals RF_{1 . . . N}may be generated, which may be filtered by a plurality of filters 520 _{1, 2, . . . , N}. The resulting N filtered signals may then be downconverted to baseband utilizing a plurality of N mixers 524 _{1, 2, . . . , N}, each of which may be provided with a carrier signal that may be generated by a local oscillator 522. The N baseband signals generated by the mixers 524 _{1, 2, . . . , N}may then be converted to digital signals by a plurality of analog to digital (A/D) converters 526 _{1, 2, . . . , N}. The N digital signals may further be processed by a spatial multiplexing baseband processor SMBB 530 to generate an output signals {circumflex over (X)}₁. . . {circumflex over (X)}_N, which are estimates of the original spatial multiplexing sub-stream signals or symbols X₁. . . X_N.
FIG. 6 is a flow diagram illustrating exemplary steps for processing signals in a communication system, in accordance with an embodiment of the invention. Referring to FIG. 6, exemplary steps may start at step 600. At step 602, a plurality of spatially multiplexed communication signals may be received in a MIMO receiver. At step 604, a plurality of control signals may be generated, which may be utilized to control at least a first portion of the received plurality of spatially multiplexed communication signals. At step 606, a phase and/or amplitude of the first signal portion may be adjusted utilizing the plurality of control signals so that the phase and/or amplitude of the first signal portion is equivalent to a second portion of the received plurality of spatially multiplexed communication signals. At step 608, the phase and/or amplitude-adjusted first portion of the received plurality of spatially multiplexed communication signals may be combined with the second portion of the received plurality of spatially multiplexed communication signals to generate a combined received spatially multiplexed communication signal. At step 610, the combined received spatially multiplexed communication signal may be subsequently processed to generate a plurality of baseband combined channel estimates of a time varying impulse response for the first and/or the second portion of the received plurality of spatially multiplexed communication signals. At step 612, the plurality of baseband combined channel estimates of a time varying impulse response for the first and/or the second portion of the received spatially multiplexed communication signal may be utilized by a single weight generator to generate a plurality of control signals. The exemplary steps may end at step 614.
Aspects of the system may comprise generating a plurality of control signals A₁₁, φ₁₁ 142 ₁₁to A_PM-1, φ_PM-1 142 _PM-1, by a weight generator SWG 140, where the control signals A₁₁, φ₁₁ 142 ₁₁to A_1M-1, φ_1M-1 142 _1M-1may be utilized to control at least a first of the plurality of received spatially multiplexed communication signals from the plurality of receive antennas 124 _{1 . . . M}. A phase and/or an amplitude of the first of the plurality of received spatially multiplexed communication signals may be adjusted by the SMBB 138 via the plurality of generated control signals A₁₁, φ₁₁ 142 ₁₁to A_1M-1, φ_1M-1 142 _1M-1, so that the phase and/or the amplitude of the first received spatially multiplexed communication signal may be equivalent or different to a phase and/or amplitude of a second received spatially multiplexed communication signal, where the phase and/or the amplitude of the first received spatially multiplexed communication signal is adjusted within a processing path used to process the first received spatially multiplexed communication signal.
The generated control signals may comprise single weight signals. The amplitude of the first received spatially multiplexed communication signal may be adjusted continuously and/or at discrete intervals. An amplifier LNA 128 may amplify the first received spatially multiplexed communication signal so that a gain of the first received spatially multiplexed communication signal may be equivalent or different to a gain of the second received spatially multiplexed communication signal. A summer 136 ₁may be adapted to combine the amplitude-adjusted first received spatially multiplexed communication signal with the second received spatially multiplexed communication signal to generate a combined received spatially multiplexed communication signal. The SMBB 138 may generate a plurality of baseband combined channel estimates of a time varying impulse response for the plurality of received spatially multiplexed communication signals and the baseband combined channel estimates of the time varying impulse response may be utilized to generate the plurality of control signals A₁₁, φ₁₁ 142 ₁₁to A_PM-1, φ_PM-1 142 _PM-1. The weight generator SWG 140 may generate the control signals utilizing one or more optimization algorithms, such as a maximum signal-to-noise ratio (SNR) algorithm, a maximum signal-to-interference-and-noise ratio (SINR) algorithm, and/or a minimum bit error rate (BER) algorithm. Choosing which adaptive algorithm to use will be based upon the implementation complexity and performance tradeoffs between the different cost functions.
Accordingly, the present invention may be realized in hardware, software, firmware or a combination of hardware, software and/or firmware. Some embodiments according to some aspects of the present invention may be realized, for example, in a centralized fashion in at least one computer system, or in a distributed fashion where different elements are spread across several interconnected computer systems. Any kind of computer system or other apparatus adapted for carrying out the methods described herein is suited. A typical combination of hardware and software may be a general-purpose computer system with a computer program that, when being loaded and executed, controls the computer system such that it carries out the methods described herein.
Some embodiments according to some aspects of the present invention may also be embedded in a computer program product, which comprises all the features enabling the implementation of the methods described herein, and which when loaded in a computer system is able to carry out these methods. Computer program in the present context may mean, for example, any expression, in any language, code or notation, of a set of instructions intended to cause a system having an information processing capability to perform a particular function either directly or after either or both of the following: a) conversion to another language, code or notation; b) reproduction in a different material form.
While the present invention has been described with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the present invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present invention without departing from its scope. Therefore, it is intended that the present invention not be limited to the particular embodiments disclosed, but that the present invention will include all embodiments falling within the scope of the appended claims.

Claims

What is claimed is:

1. A method, comprising:

adjusting a phase of a first spatially multiplexed communication signal so that the phase of the first spatially multiplexed communication signal is equivalent to a phase of a second spatially multiplexed communication signal;

combining the first and second spatially multiplexed communication signals to form a combined spatially multiplexed communication signal; and

generating a control signal based on the combined communication signal.

2. The method of claim 1, further comprising generating a channel estimate using the first and second spatially multiplexed communication signals.

3. The method of claim 2, wherein the phase of the first spatially multiplexed communication signal is adjusted based on the generated channel estimate.

4. The method of claim 1, further comprising continuously adjusting the phase do the first spatially multiplexed communication signal.

5. The method of claim 1, further comprising adjusting the phase of the first spatially multiplexed communication signal at discrete intervals.

6. The method of claim 1, further comprising adjusting an amplitude of the first spatially multiplexed communication signal to be equivalent to the amplitude of the second spatially multiplexed communication signal.

7. The method of claim 1, wherein the channel estimate is also based on a third spatially multiplexed communication signal.

8. The method of claim 1, further comprising receiving a plurality of spatially multiplexed communication signals.

9. The method of claim 8, wherein the channel estimate is a baseband combined channel estimate for the plurality of spatially multiplexed communication signals.

10. The method of claim 1, wherein the control signal is generated utilizing an optimization algorithm comprising at least one of a maximum signal-to-noise ratio (SNR) algorithm, a maximum signal-to-interference-and-noise ratio (SINR) algorithm, and a minimum bit error rate (BER) algorithm.

11. A system, comprising:

one or more processors and/or circuits configured to:

adjust a phase of a first spatially multiplexed communication signal so that the phase of the first spatially multiplexed communication signal is equivalent to a phase of a second spatially multiplexed communication signal;

combine the first and second spatially multiplexed communication signals to form a combined spatially multiplexed communication signal; and

generate a control signal based on the combined communication signal.

12. The system of claim 11, wherein the one or more processors and/or circuits are further configured to generate a channel estimate using the first and second spatially multiplexed communication signals.

13. The system of claim 12, wherein the one or more processors and/or circuits are further configured to adjust the phase of the first spatially multiplexed communication signal is based on the generated channel estimate.

14. The system of claim 11, wherein the one or more processors and/or circuits are further configured to continuously adjust the phase do the first spatially multiplexed communication signal.

15. The system of claim 11, wherein the one or more processors and/or circuits are further configured to adjust the phase of the first spatially multiplexed communication signal at discrete intervals.

16. The system of claim 11, wherein the one or more processors and/or circuits are further configured to further adjust an amplitude of the first spatially multiplexed communication signal to be equivalent to the amplitude of the second spatially multiplexed communication signal.

17. The system of claim 11, wherein the one or more processors and/or circuits are further configured to generate the channel estimate based on a third spatially multiplexed communication signal.

18. The system of claim 11, wherein the one or more processors and/or circuits are further configured to receive a plurality of spatially multiplexed communication signals.

19. The system of claim 18, wherein the one or more processors and/or circuits are further configured to generate the channel estimate as a baseband combined channel estimate for the plurality of spatially multiplexed communication signals.

20. A non-transitory computer-readable medium configured to store computer instructions that, when executed by a computer, cause the computer to perform steps comprising:

generating a control signal based on the combined communication signal.